spring security中自定义authenticationProcessingFilter

public Authentication attemptAuthentication(
			HttpServletRequest httpServletRequest)
			throws AuthenticationException {
		String check_code = httpServletRequest.getParameter("j_checkcode");
		String sys_code = (String) httpServletRequest.getSession()
				.getAttribute(checkCodeName);

		if (sys_code == null) {
			throw new AuthCodeValidationException("验证码不正确");
		} else if (!sys_code.equals(check_code)) {
			String username = obtainUsername(httpServletRequest);
			httpServletRequest.getSession().setAttribute(
					SPRING_SECURITY_LAST_USERNAME_KEY, username);
			// 用户输入的值与看到的不一致,抛出异常
			throw new AuthCodeValidationException("验证码输入不正确");
		}
		return super.attemptAuthentication(httpServletRequest);
	}